1. Field of the Invention
The present invention relates to a lithographic apparatus, a coil assembly, a positioning device including a coil assembly, and a device manufacturing method using a positioning device.
2. Discussion of the Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (IC's). In that circumstance, a patterning device, such as a mask, may be used to generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g., including part of one, or several, dies) on a substrate (e.g., a silicon wafer) that has a layer of radiation-sensitive material (resist). In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through the beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction.
In a scanner, portions of the substrate are scanned successively. In between a warming of a portion and a scanning of a next portion of the substrate, a movement is made to position the substrate and the patterned beam relative to each other such that scanning of The next portion of the substrate can start. The scanning movement can be performed by moving the substrate, or by moving a suitable pan of the illumination system and/or a suitable part of the projection system. Also, it is possible that each of these elements or any suitable combination thereof is moved thus achieving a desired scanning of the patterned beam relative to the substrate. The moving of the different elements with respect to one another is generally performed using positioning devices. Amongst others, use is made of linear and planar positioning devices.
Linear positioning devices may be applied for moving the substrate table relative to the lithographic apparatus, or moving the patterned beam relative to the lithographic apparatus. In other embodiments of lithographic apparatuses, planar positioning devices may be applied for positioning the substrate table in two directions, e.g. a plane. Other elements of the lithographic apparatus may also be moved by positioning devices.
In the field of manufacturing IC's, it is desirable to increase the speed of production of integrated circuits. One possibility of increasing the speed of production is to move the moveable parts of the lithographic device with respect to one another at a higher speed. This higher speed calls for an improvement of the dynamic behavior of the positioning systems with which the different elements of a lithographic device are moved.
If the maximum accelerations with which positioning devices can displace loads are increased, a movement from a first location to a second location can be conducted at a higher average speed. One possible way to improve the dynamic behavior of a positioning device is to construct the moving part thereof with less mass. If the mass of a positioning device is decreased, the accelerations that it can achieve while applying the same force will be greater, hence enabling movements to be performed at a higher speed. Alternatively, when the same accelerations are performed, the carrying load of the positioning device can be greater.
Linear and planar positioning devices generally include a first part and a second part which are moveable with respect to one another in at least one direction. The first part generally includes an array of fixed magnets arranged in a pattern, having an orientation of the magnetization field which is perpendicular to the direction of movement. Typically, a number of N and S magnets are arranged in an alternating manner, having a distance between each N-pole and S-pole which is indicated as the magnetic pole pitch.
The second part generally includes an assembly of coils, constructed in a common plane with respect to one another. The coils include current conductors in the form of one or more windings. When a current flows in a current conductor, the flux density of the magnetic field created by the magnets exerts a Lorentz force on the current conductors of the coils. The direction of the Lorentz force is oriented perpendicular to the direction of the magnetic field and perpendicular to the extension of the current conductor.
Known positioning devices generally include coil assemblies including two or three coils. The coils generally have substantially the shape of a closed loop, defining an open area within the coil. The coils do not have an iron core, thereby avoiding any magnetic forces between the coil assembly and the array of magnets when no currents are conducted through the coils. A coil generally includes two main current conductor sections, connected to one another by two other sections. In known devices, the coils are positioned in an overlapping configuration, wherein one main current conductor section of a first coil overlaps the open area of a second coil. In order to connect this main current conductor section of the first coil to the rest of the first coil, the first coil is required to cross the second coil in a crossover section thereof outside the main current conductor sections. In the known positioning devices, crossover sections of the first and second coil are stacked on top of one another, thereby increasing the height of a coil assembly at the crossover sections.
Generally, the coil assembly is enclosed in a second enclosing material which keeps the coils in a fixed position relative to one another. Epoxy resin is often used as his second enclosing material. Other materials are also used. If the total height of the coil assembly is large, a relatively large amount of second enclosing material is also necessary in order to enclose the entire coil assembly. This will increase the mass of the coil assembly, leading to a poorer performance in terms of dynamic behavior.